1. Field of the Invention
This invention relates to an apparatus and method for providing color photographic images, and particularly such images produced from a digital or analog data base utilizing a laser radiation source.
2. Description of the Prior Art
U.S. Pat. No. 4,346,401 discloses apparatus and a method for producing a full color, continuous tone image on a color film utilizing three gaseous lasers, each laser emitting light in the visible region of the electromagnetic spectrum corresponding to one of the three primary colors. Any color of the visible portion of the electromagnetic spectrum may be obtained on the film, upon development, and continuous toning of the colors is produced by modulating the output of the gaseous lasers to vary the intensity of the light emitted by the lasers and thereby the exposure of the color film and the density of the colors produced in the film upon development.
This system is effective to produce color images but has three major drawbacks. First, a helium-neon laser, an argon laser and a helium-cadmium laser must be provided, each of which is relatively expensive, has a relatively short life and requires special care and handling. Second, an external modulator must be provided for each laser since the intensity of the light emitted by each laser cannot be directly modulated. External modulators are also expensive and multiply the cost of the system. Third, conventional color film is utilized and thus the imaging operation must be performed in visible light-proof conditions to avoid exposure of the film. Additionally, special dark rooms must be provided for the imaging operation and control over ingress and egress to the room must be maintained to prevent inadvertent admission of outside light.
U.S. Pat. No. 4,416,522 discloses apparatus and a method which eliminates the disadvantages associated with the use of conventional color film. This patent utilizes a color film which produces visible colors upon exposure to radiation in the non-visible portion of the spectrum. Thus, the resulting dye colors in the developed film belong to a spectrum (visible) different from the spectrum (non-visible) which exposes the film. With such a film, one can select exposing radiation in the various portions of the non-visible spectrum and expose the film in daylight to produce color images in the visible portion of the spectrum when the film is developed. The film is exposed by a lamp which emits a broadband beam including multiple wavelengths of non-visible radiant energy to which the emulsion layers of the film are variously sensitive. Exposure of the film to a particular wavelength or radiation is accomplished by interposing a filter between the lamp and the film which filters out all radiation except that at the desired wavelength. Variations in the intensity of the radiation beam produced by the lamp to vary the exposure of the film and the density of the color produced is achieved by increasing or decreasing the speed of the film relative to the exposing beam and thus changing the duration of contact between the beam and a particular portion of the film.
Two major disadvantages are associated with this system. First, changing a filter to produce individual colors is necessarily slow in itself and also slows down the process because the surface of the film must be covered three times to produce the three primary colors in the film upon development. Second, modulation of the intensity of the exposing beam by increasing or decreasing the relative speed of the beam and the film is expensive since servo motors and their associated controls must be provided for each of the x and y coordinates of the film surface.
With respect to photosensitive films, dyes which have been capable of sensitizing silver halide emulsions to infrared region os the electromagnetic spectrum have been known for many years. Merocyanine dyes and cyanine dyes, particularly those with longer bridging groups between cyclic moieties have been used for many years to sensitize silver halide to the infrared. U.S. Pat. Nos. 3,619,154, 3,682,630, 2,895,955, 3,482,978, 3,758,461 and 2,734,900; and U.K. Patent Nos. 1,192,234 and 1,188,784 disclose well-known classes of dyes which sensitize silver halide to portions of the infrared region of the electromagnetic spectrum. U.S. Pat. No. 4,362,800 discloses dyes used to sensitize inorganic photoconductors to the infrared, and these dyes are also effective sensitizers for silver halide.
With the advent of lasers, and particularly solid state laser diodes emitting in the infrared region of the electromagnetic spectrum (e.g. 780 to 1500 nm), the interest in infrared sensitization has greatly increased. Many different processes and articles useful with laser diodes have been proposed. U.S. Pat. No. 4,416,522, for example, proposes daylight photoplotting apparatus for the infrared exposure of film. This patent also generally proposes a film comprising three emulsion layers sensitized to different portion of non-visible portions of the electromagnetic spectrum including the infrared. The film description is quite general and the concentration of imagewise exposure on each layer appears to be dependent upon filtering of radiation by the apparatus prior to its striking the film surface.